Extension Storage API: expose storage quota information to extensions, via:

chrome/browser/extensions/settings/settings_leveldb_storage.cc

Index: chrome/browser/extensions/settings/settings_leveldb_storage.cc
diff --git a/chrome/browser/extensions/settings/settings_leveldb_storage.cc b/chrome/browser/extensions/settings/settings_leveldb_storage.cc
index b768e291604b710bf0e12a52d50281705ab77ba7..a511f6b4d3e9dc7ec1129b6ce3c812b39d2f8f2f 100644
--- a/chrome/browser/extensions/settings/settings_leveldb_storage.cc
+++ b/chrome/browser/extensions/settings/settings_leveldb_storage.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -95,6 +95,12 @@ SettingsLeveldbStorage::~SettingsLeveldbStorage() {
   }
 }
 
+size_t SettingsLeveldbStorage::GetBytesInUse() {
+  // Let SettingsStorageQuotaEnforcer implement this.
+  NOTREACHED() << "Not implemented";
+  return 0;
+}
+
 SettingsStorage::ReadResult SettingsLeveldbStorage::Get(
     const std::string& key) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));